The present invention relates to a sound pickup device that picks up sound from a desired area using a microphone array, and to a voice conference apparatus, to which the sound pickup device is applied.
In the past, voice conference apparatuses have been proposed as apparatuses for performing a voice conference among remote places (for example, see Patent Documents 1 and 2). The voice conference apparatus has a function of picking up sound of attendants of a voice conference and transmitting sound to remote voice conference apparatuses.
There are often many attendants in the conference, and thus the voice conference apparatus needs to pick up sound of each attendant at the same level and at a level as high as possible. In addition, when the attendant moves, the voice conference apparatus needs to prevent the attendant from departing from a sound-pickup area despite the attendant's movement. Further, when there is often a noise source, such as a projector and so on, in a conference room, the voice conference apparatus needs to set a sound-pickup area so that noise is not picked up.
The voice conference apparatus disclosed in Patent Document 1 includes microphones provided at four corners of a housing having a substantially square shape, thereby picking up sound signals in different directions. The voice conference apparatus disclosed in Patent Document 2 delays the sound signals picked up by two non-directional microphones on left and right sides for an appropriate time and synthesizes the delayed sound signals, such that sound of a plurality of speakers can be extracted at a high gain.    Patent Document 1: JP-A-8-298696    Patent Document 2: JP-A-5-158492
However, in the apparatus disclosed in the Patent Document 1, the four microphones simply pick up the sound signals in different directions. Accordingly, when a noise source exists in a conference room, the apparatus cannot avoid picking up noise from the noise source. Further, it is impossible to increase levels of the picked-up sound signals by synthesis or the like.
In the apparatus disclosed in the Patent Document 2, it is possible to pick up sound (a speaker's speaking) generated at a predetermined position at a high level by delaying the sound signals picked up by the two microphones and synthesizing the delayed signals. In this apparatus, however, the position where a high-level signal can be obtained by synthesis is in a narrow range of a spot shape. Accordingly, when the speaker moves, it is difficult to follow the movement of the speaker (an attendant in a conference). In addition, when a plurality of attendants speak at the same time, a plurality of sets of delay circuits are needed to pick up sound at the same time. As a result, the configuration of the apparatus becomes complex.